1. Field of the Invention
The present invention relates to a fusing unit to heat and press a toner image transferred onto paper, and more particularly, to a fusing unit used with a color laser printer.
2. Description of the Related Art
In general, color laser printers develop an electrostatic latent image formed on a photosensitive body with toner in a powder state, transfer the developed image onto paper, heat and press the transferred image, and fuse the heated and pressed image on the paper. A fusing unit of the color laser printers which performs a fusing operation has a structure schematically shown in FIG. 1. Two rollers 10 and 20, in which heaters 11 and 21 are respectively disposed, are in close contact with each other and rotate while a sheet of paper 1 passes therebetween. In this procedure, a toner image formed on the sheet of paper 1 is heated by heat generated by the heaters 11 and 21 and pressed by an adhesion force formed between the two rollers 10 and 20, and then is completely fused on the sheet of paper 1. In general, an upper roller 10 is referred to as a heat roller, and a lower roller 20 that is in close contact with the heat roller 10 by a spring 25 is referred to as a pressure roller. Outer circumferences of aluminum cores 12 and 22 of the heat roller 10 and the pressure roller 20 are respectively covered with silicon rubber layers 13 and 23, and Teflon layers 14 and 24 are respectively coated on the silicon rubber layers 13 and 23.
In the conventional color laser printer, metallic ball bearings 30, as shown in FIG. 2, are generally used to support the heat roller 10 and the pressure roller 20. In other words, the cores 12 and 22, acting as rotating axes of the two rollers 10 and 20, are rotatably supported to be centered on a frame 40 via a respective metallic ball bearing 30 and are rotated by a motor (not shown).
However, in addition to high manufacturing costs, since it is difficult to process the metallic ball bearings 30, the metallic ball bearings 30 are formed into a ring-shape. Thus, a support structure to support the metallic ball bearings 30 is defined by a circular hole indicated by a reference numeral 41 shown in FIG. 2. As printers recently become smaller, the shape of a fusing unit also becomes very complicated and compact in consideration of shapes of other peripheral structures and a combinational relationship therebetween. To this end, the shape of a frame 40, in which a support structure is provided, needs to be optimized. However, due to the restriction on the shape of the metallic ball bearings 30, it is difficult to optimize the shape of the frame 40 and to implement a compact fusing unit.